There is a look at the next five group topics in the new numbering system. The Head Group (1500) is the last expensive component of building a long block. The other groups here are mostly made of parts that came with your core engine and basic labor you can add yourself. Getting through groups 1000-1900 will give you an engine that is internally complete, and it is the lion’s share of the money spent building the engine
Later groups address oil systems, starters, ignitions, etc, all external systems that are bolted on your long block. All of this can be purchased as you go, adjusted on your own timeline and budget. The later parts are intentionally broken down into affordable blocks that can be installed at one time, like the $516 starter system group (2400).